Many membrane proteins mediate bacterial pathogenesis and host interactions. These proteins are not the more commonly investigated channels, transporters, and GPCRs and, therefore, provide new knowledge about membrane protein structure, function, and dynamics. Bacterial membrane proteins are targets of antibiotics for which resistance is a great threat. In addition, bacterial membrane proteins that interact with hosts have evolved functions that are attractive to therapeutic delivery technologies (e.g. receptor-mediated uptake). This MIRA application outlines our recent endeavors in understanding several different bacterial membrane proteins, as well as, fruitful collaborations bridging biophysics to different biomedical fields. Opa proteins from Neisseria gonorrhoeae and N. meningitidis are outer membrane proteins that bind to various host receptors that induce engulfment of the bacterium. Several of these receptors are overexpressed in cancers and may provide a target for therapeutic delivery. Knowledge of the structure, dynamics, and specific interactions of Opa proteins and receptors will be used to design targeted liposome delivery to human cells. We have begun to understand the Opa structure and have preliminary data on the interactions between Opa and the receptor CEACAM1. In addition, we have successfully created Opa-liposomes that induce receptor-mediated phagocytosis. Future directions focus on a multidisciplinary approach to understanding the determinants of Opa-receptor selectivity and engineer therapeutic delivery liposomes based on the interaction. Another function of interest to therapeutic delivery, is cellular tracking and controlling cellular fate. IncA, from Chlamydiae, hijacks host trafficking by interacting with host SNAREs allowing the bacterium to avoid lysosomal degradation. We propose a variety of biophysical and structural approaches to understanding the structure- function relationship of IncA and interactions with itself and SNAREs in order to design intracellular delivery systems that can avoid lysosomal degradation. Distinct from our research with Opa and IncA, we have begun to investigate potential antibiotic targets to help combat the increase in resistant bacteria. The signal peptidase II, LspA, is a potential target because it is found in all Gram-negative bacteria and not humans. Globomycin was isolated and the antibiotic activity was identified in 1978. Although the synthesis and structure are now known, globomycin has not become a therapeutic. We aim to explore the binding and inhibition of LspA with globomycin-like peptides in order to identify viable antibiotics for Gram-negative bacteria. The results of this proposal with provide unique knowledge and insights about bacterial membrane proteins and their roles in pathogenesis using biophysical approaches and will develop strategies for the design of therapeutics to treat bacterial infections and a variety of human cancers involving CEACAM receptors.